A drive force transmission apparatus drives a subject mechanism, which is connected to an output shaft of the drive force transmitting apparatus, by transmitting rotation of an input shaft, which is driven with a drive force of, for example, an electric motor, to the output shaft at a rotational speed that is the same, decreased or increased relative to a rotational speed of the input shaft. In a typical drive force transmission apparatus, an input-to-output speed ratio (also referred to as a speed change ratio), which is a ratio between a rotational speed of the input shaft and a rotational speed of the output shaft, and an output characteristic of a transmitted torque, which is transmitted from the input shaft to the output shaft, are constant regardless of the rotational direction of the input shaft. However, in some cases, it is required to provide different output characteristics between the normal rotation and the reverse rotation or between forward movement and backward movement of an actuator, which serves as the subject mechanism.
For example, a loading and unloading lift requires the low speed and high torque at the time of lifting up and requires the high speed without requiring a torque at the time of lifting down. A winch requires the low speed and high torque at the time of winding up (pulling in) and requires the high speed without requiring a torque at the time of winding out (letting out). A clamp requires the high clamping force at the low speed at the time of clamping and requires the high speed without requiring a clamping force at the time of unclamping. A clutch requires the high torque and low speed at the time of compressing a spring and requires the low torque and high speed at the time of releasing in a direction of the spring force.
Furthermore, in a variable compression ratio engine, which can change a compression ratio thereof, the low speed and high torque is required at the time of changing from a low compression ratio side to a high compression ratio side, and the high speed is required without requiring a torque at the time of changing from the high compression ratio side to the low compression ratio side.
As discussed above, in the cases where the required characteristics change between the normal rotation and the reverse rotation or between the forward movement and the backward movement, the actuator having the fixed input-to-output speed ratio needs to sacrifice one of the characteristics or needs to incases the output and/or size of the motor and/or the actuator.
a technique of a transmission, such as an automatic transmission of a vehicle, which uses electronic control, is known as an apparatus and/or a method, which changes the output characteristic between the normal rotation and the reverse rotation or between the forward movement and the backward movement. Also, it is known to mechanically or electrically sense the rotational direction and to select one of different drive force transmission paths, which have different gear ratios, respectively. For example, Japanese Unexamined Patent Publication JP2006-234062A recites a two-speed transmission apparatus, which can rotate in both of a normal rotational direction and a reverse rotational direction. This two-speed transmission apparatus includes an electromagnetic clutch, which can electromagnetically couple and decouple between an output shaft of a drive device and an internal gear of a speed reducing planetary gear mechanism.
There are also disclosed the following techniques as the other apparatus and/or method.
Japanese Patent JP4333129B2 recites a variable compression ratio engine. At this engine, two one-way clutches are used to change between two drive force transmission paths. According to Japanese Patent JP4333129B2, when the drive force transmission path of a high speed reducing ratio is selected, the output of the low rotational speed and high torque is obtained. In contrast, when the drive force transmission path of a low speed reducing ratio is selected, the output of the high rotational speed and low torque is obtained.
Japanese Unexamined Patent Publication JP2009-079408A teaches an opening/closing body drive apparatus. In this opening/closing body drive apparatus, two one-way clutches are used to form the two drive force transmission paths and to enable selection between the two drive force transmission paths, like in Japanese Patent JP4333129B2.
Japanese Unexamined Patent Publication JP2004-239326A (corresponding to US2004/0152556A1) teaches an automatic reducing-ratio changing apparatus. In this automatic reducing-ratio changing apparatus, a high torque is generated at a terminal end of a forward path (outward route) of an actuator, and thereafter lock levers are moved by an abutment force to change the speed reducing ratio (reducing-ratio), so that the actuator is displaced at a high speed in the backward path (homeward route).
Japanese Unexamined Patent Publication JPH07-071558A (corresponding to U.S. Pat. No. 5,557,987) teaches a rotation transmission apparatus. In this rotation transmission apparatus, ratchets are used to select a drive force transmission path based on a rotational direction.
Japanese Unexamined Utility Model Publication JPH06-8945U teaches an automatic winding speed change mechanism for a camera. This automatic winding speed change mechanism includes an electric motor and two transmission gear systems, and a switching gear is moved upward or downward according a winding load to change a drive force transmission path, thereby automatically changing a winding speed.
However, the apparatus, which uses the electronic control, and the apparatus, which uses the mechanical or electric sensing and the drive force switching mechanism, are complicated and have the increased sizes, thereby resulting in the high costs. For example, the apparatus of Japanese Unexamined Patent Publication JP2006-234062A has the increased number of components due to the addition of a solenoid of the electromagnetic clutch and a control device, thereby resulting in the increased costs. Furthermore, a circuit, which controls the solenoid synchronously with the rotational direction of the motor, is required. A sensor and a control element are required, so that fine movement is difficult, and the operation may possibly become unreliable.
In Japanese Patent JP4333129B2 and Japanese Unexamined Patent Publication JP2009-079408A, the two one-way clutches, which limit opposite rotations, respectively, are used. The one-way clutches respectively transmit rotational forces to the two transmission paths, which have the different input-to-output speed ratios, respectively. In this way, the input-to-output speed ratio is changed according to the rotational direction. However, as discussed below, this structure cannot implement the normal rotation and the reverse rotation.
For example, in Japanese Unexamined Patent Publication JP2009-079408A, the two one-way clutches, i.e., a first one-way clutch and a second one-way clutch are provided to the output shaft. The first one-way clutch and the second one-way clutch limit opposite rotations, respectively, which are opposite to each other. The first one-way clutch drives an opening side drive gear, and the second one-way clutch drives a closing side drive gear. The opening side drive gear and the closing side drive gear are engaged with an opening side driven gear and a closing side driven gear, respectively, which are fixed to a common intermediate shaft.
With the above structure, it is now assumed that the output shaft is rotated in a drive force transmitting direction of the first one-way clutch, so that the common intermediate shaft is rotated through the gear. Then, the rotation of the intermediate shaft is transmitted to the closing side drive gear through the closing side driven gear, so that a rotational force is applied to the closing side drive gear in a rotational direction that is the same as a rotational direction of the output shaft. Here, in a case where a rotational speed of the closing side drive gear is higher than a rotational speed of the output shaft, it corresponds to a state, in which the output shaft is rotated in an opposite rotational direction that is opposite from a rotational direction of the closing side drive gear. The state, in which the output shaft is rotated in the opposite rotational direction, is a drive force transmitting state of the second one-way clutch. Therefore, the first one-way clutch and the second one-way clutch are simultaneously held in the drive force transmitting state. As a result, deadlock occurs, i.e., the drive force transmission systems interfere with each other due to the drive force transmissions at the different input-to-output speed ratios. Therefore, this mechanism cannot be properly operated, i.e., is inoperable.
Furthermore, various operational patterns have been checked for the case, in which the two one-way clutches are constructed to limit the rotations in the same rotational direction, the case, in which an inner race of the one-way clutch is driven, and the case in which an outer race of the one-way clutch is driven. Based on a result of this checking, it has been found that the deadlock occurs in all of the patterns, or the two one-way clutches are freed, i.e., are decoupled, and thereby the output shaft is not rotated. That is, the simple combination of the two one-way clutches cannot form the mechanism, which can change the input-to-output speed ratio between the time of normal rotation and the time of reverse rotation.
Furthermore, in Japanese Unexamined Patent Publication JP2004-239326A (corresponding to US2004/0152556A1), when the operation is reversed to the backward path (homeward route) before reaching the terminal end of the forward path (outward route), the speed change cannot be made.
In Japanese Unexamined Patent Publication JPH07-071558A (corresponding to U.S. Pat. No. 5,557,987), a lost torque is generate between an input shaft and an output shaft due switching of the ratchets. Also, a ratchet system, which includes the ratchets, needs to be installed to a portion of the apparatus, which is connected to an inside of the drive shaft or the drive shaft itself. Therefore, the apparatus cannot be made compact or cannot have a simple structure. Furthermore, a good rotational balance is difficult to implement, so that it is not suitable for the high speed rotation. In addition, a ratchet fitting portion is limited to a circumferential portion of the corresponding gear, so that the amount of the drive force transmission may possibly become short relative to the size of the entire apparatus.
In the speed change mechanism of Japanese Unexamined Utility Model Publication JPH06-8945U, in the middle of moving the switching gear in the upward movement or the downward movement, there is a period, during which the drive force cannot be conducted to any of the systems. Furthermore, the switching gear is moved upward or downward while being rotated, so that at the time of contacting the switching gear and the transmission gear with each other, teeth of the switching gear and teeth of the transmission gear may not possibly be engaged with each other and may possibly be repelled each other. Therefore, particularly, this cannot be applied to an apparatus, which rotates at a high rotational speed.